One of the teenagers came to school with bruises, but wouldn’t say how they occurred. Her angry younger sister was skipping classes, her grades plummeting. Both were desperate to leave home. And hovering over everything was the spectre of a controlling, often violent father, of whom they were clearly terrified.

In short, what appears to have transpired was a profound and – it’s alleged– ultimately murderous clash of cultures.

Listening to teachers and social workers on Thursday, the jury weighing the fate of three Afghan-Canadians accused of committing multiple so-called honour killings heard a wealth of testimony pointing to a deeply dysfunctional, male-dominated Montreal household.

The four bodies were discovered in a car at the bottom of a lock on the Rideau Canal just east of Kingston in June, 2009.

The jury has already heard that Sahar attempted suicide, and fresh testimony Thursday underscored the depths of her misery and fear, and the similar plight of her younger sister Geeti. Both attended Antoine de Saint-Exupery high school in the Montreal borough of St. Leonard.

Teacher Claudia Deslauriers told the jury of seeing bruises, scratches and scars on Sahar’s forearms. When she asked the teen what had happened, “she didn’t say anything,” Ms. Deslauriers testified.

Ms. Deslauriers also recounted meeting the children’s “really angry” mother, Ms. Yahya, who demanded to know if Sahar had a boyfriend, and if Ms. Deslauriers had seen her kissing him. The teacher said no, she had not, which was false, because, “I didn’t want her to have any problems at the house.” Ms. Yahya told the teacher she could not tolerate her daughter kissing a boy “because it did not fall within her values,” Ms. Deslauriers testified.

Also testifying Thursday was social worker Stephanie Benjamin, summoned by the school psychologist just weeks before Sahar and the others died.

“She feared being beaten by her father, who had just come back to Canada [from a business trip]” Ms. Benjamin said of Sahar, who was anxious to leave home and get a job. Her long-term hope was to become a gynecologist and work in Afghanistan, but her immediate need was to get away from her father and older brother, Hamed, who more than once had physically abused her – on one occasion by flinging scissors at her from across the table. “She was asking me to help,” Ms. Benjamin testified.

It was not only her parents and older brother whom Sahar feared, the trial heard. She worried about one of her other male relatives telling the adults that she was associating with boys at school. “She was afraid [the relative] would tell her father she was a whore,” former teacher Antonella Enea told the jury.

“She said she couldn't live a normal life – to see her friends, things of that nature,” Ms. Enea said of Sahar, who attended classes for new immigrants at the school. Geeti, too, showed signs of being profoundly unhappy at home and afraid of her father, manifested in poor attendance and mood swings, the jury heard.

On two separate occasions – in 2008 and then in 2009, just weeks before the teens died – child-welfare authorities in Montreal were contacted. Both times there was no intervention. Part of the difficulty, the trial has been told, was that Sahar and Geeti were reluctant to confront their domineering father.

The trial is in its sixth week, and the prosecution is expected to wrap up its case on Dec. 5.

The older victim in the Nissan Sentra found at the bottom of the lock, Rona Amir Mohammad, had rejoined the rest of the family in Canada in 2007 after living with them for many years in Dubai. Ostensibly, she was Mr. Shafia’s cousin, but she was in fact his first wife, living in a clandestine polygamous marriage.

Travelling in two vehicles, a Nissan and a Lexus, the 10-member party had been returning home to Montreal after a short vacation in Niagara Falls. The three defendants told police a dreadful accident had taken place during an overnight stay at a Kingston motel after Zainab and the other three victims had taken the Nissan for a joyride.

Police swiftly suspected murder, however, and the prosecution thesis is that the so-called honour killings were committed in efforts to cleanse the family of the rebellious, supposedly immoral conduct of the three Shafia sisters, in particular the dating habits of the eldest two.

Under cover of darkness, the Nissan was pushed into the lock by the Lexus, it’s alleged.

Ms. Mohammad was not the biological mother of any of the seven Shafia siblings, but she was close to Sahar and was slain after years of mistreatment, the prosecution contends.

In earlier evidence Thursday, a police videotape of Mr. Shafia being interviewed one day after the four bodies were discovered – three weeks before charges were laid – showed that almost from the outset detectives suspected that damage to the rear of the sunken Nissan had been caused by the Lexus.

Detective Constable Steve Koopman was seen seeking Mr. Shafia’s permission to examine the Lexus. The previous day, Hamed Shafia had driven it back to Montreal, where he said he had had a single-vehicle accident in a parking lot. On the face of things, that would account for the car’s smashed headlight, pieces of which were later located at the lock. But the police were suspicious.

In the interview, Mr. Shafia looks surprisingly composed in light of the fact that three of his daughters and first wife had just died. And he readily agreed to Det. Constable Koopman’s request.

“I don’t know how they came to be in the water,” he told the detective. “If someone choked them, if they have swallowed some drug, if they have gone crazy – I want to know.”

Mr. Shafia was also advised that even though he was not considered a suspect, he was entitled to a lawyer, and if necessary, legal aid. In response he asked whether legal aid was free.